How Can I Check Mac No-access

Understanding Internet Addressing

When connecting to the Internet, you are assigned a Public IPv4 address, such as 161.239.159.197, or an IPv6 address, like 2000:fb54:3634:1607:6674:5f2f:69ef:dda7. These addresses can be verified by visiting https://test-ipv6.com/. However, for those who are not well-versed in technology, conveying and using these addresses, or even MAC addresses like e0:33:0a:4e:e1:1f, can be prone to errors and become complex quickly. Moreover, this method does not provide any historical data, particularly when dealing with past issues.

Navigating the World Wide Web

To access a website like https://armstrong.co, you begin by accessing a DNS server to convert the host portion (armstrong) combined with the Top Level Domain (co) of the URL into an IP address, such as 162.139.74.49. Your computer and browser include their respective types in all web requests, for example:
Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36

Understanding Default Gateway Functionality

The default gateway is typically an automatically configured address provided through DHCP. You are assigned a default gateway, such as 172.31.94.126 (although they usually end in .1 or .254 based on the scope size), to which your computer sends all its traffic to be routed onward. More information about IPv6 can be found in our in-depth article on how-to-fix-ipv6-connectivity/, or you can check on Mac or Linux using this command:

IPv4 Routes and the Host IPv4 Route Table (inc. VPN)

netstat -rn -f inet | egrep -i "default|0/1|128.0/1"

0/1      172.18.12.193  UGScg  utun3
default  172.31.94.126    UGScg  en0
128.0/1  172.18.12.193  UGSc   utun3

Note: We are not just looking for the default but also for any VPN that overrides the public v4 address space.

IPv6 Routes and the Host IPv6 Route Table (inc. VPN)

netstat -rn -f inet6 | egrep -i "default|2000::/3"

If you have IPv6 active the above should return at least one route (as per below) via a known interface such as “en0 " on a Mac.

default   fe80:2655:d097:9192:8caf%en0  UGcg   en0
default   fe80::%utun0                   UGcIg  utun0
default   fe80::%utun1                   UGcIg  utun1
default   fe80::%utun2                   UGcIg  utun2
2000::/3  utun3                          USc    utun3

Note: We are not just looking for the default but also for any VPN that overrides the public v6 address space.

Debugging DHCP for both IPv4 and IPv6

To get a look at the low level DHCP configuration (Mac/Linux):

ipconfig getpacket en0

...
domain_name_server (ip_mult): {219.56.119.200, 122.196.80.137}
end (none):
...

So, in the above we are not getting IPv6 DNS servers from the DHCPv4 reply but…

ipconfig getv6packet en0

DHCPv6 REPLY (7) Transaction ID 0x80940b Length 76
Options[4] = {
  CLIENTID (1) Length 14: DUID LLT HW 1 Time 668691856 Addr e0:33:0a:4e:e1:1f
  DNS_SERVERS (23) Length 32: 2606:4700:4700::1111, 2001:4860:4860::8844
  DOMAIN_LIST (24) Length 0:  Invalid
  SERVERID (2) Length 10: DUID LL HW 1 Addr 42:7e:63:53:c5:f1
}

Troubleshooting Wired and Wireless Connections

When it comes to sending data to your router, you may be using either a wired or a wireless (Wi-Fi) medium at the physical and data layer.

Tips for Fixing Issues on Apple macOS / OSX

Regardless of whether you are using OSX/macOS versions such as 10.12.6, 11.1.5, or 12.1.7, there are various troubleshooting tools available. However, manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes essential, especially for teams that adopt remote work and Work From Anywhere (WFA).

Pre-Installed Scripts That May Be Useful

A valuable tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI, along with the option to generate specific logs for troubleshooting. For a more comprehensive approach, the sysdiagnose tool can be used to generate a wide array of logs, although many of them are only relevant to a specific point in time, similar to wdutil.

Running sudo nohup /usr/bin/sysdiagnose -u & in the background will generate logs in /var/tmp/<blah>.tar.gz. For an interactive execution (despite minimal interaction), you can run sudo /usr/bin/sysdiagnose, which will display a privacy warning. When not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp using Finder with Cmd+Shift+G. However, be cautious of the file sizes, which can be around 300MB or so.

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